Electric current detector and core component used therefor

ABSTRACT

In an electric current detector according to the present invention, an annular core  2  having a magnetic gap G and a Hall element  41  which is located in the magnetic gap of the core  2  and detects a magnitude of an electric current passing through the core  2  are arranged in an outer case  1 . Here, in the core  2 , a mold resin portion  3  which covers a surface of the core  2  over part of an overall length along a magnetic path thereof is molded at one or a plurality of portions along the magnetic path to configure an integral core component, the core component being fixed into the outer case  1  in a state where a surface of the mold resin portion  3  makes contact with an inner surface of the outer case  1.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.14/674,716, filed on Mar. 31, 2015, and wherein U.S. application Ser.No. 14/674,716 is a divisional of U.S. application Ser. No. 13/575,805,filed on Jul. 27, 2012, and wherein U.S. application Ser. No. 13/575,805is a national stage application filed under 35 U.S.C. § 371 ofInternational Application No. PCT/JP2010/068553, filed Oct. 21, 2010,which is based upon and claims the benefit of priority of the priorJapanese Patent Application No. 2010-016117, filed on Jan. 28, 2010, theentire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an electric current detector whichdetects a magnitude of an electric current by using an electromagneticconversion element such as a Hall element, and a core component used forthe electric current detector.

BACKGROUND ART

As shown in FIG. 9, there has been known such an electric currentdetector in which a core (7) having a magnetic gap G and a printedcircuit board (4) to which a Hall element (41) is attached areaccommodated in an outer case (6), the Hall element (41) beinginterposed in the magnetic gap G of the core (7).

When an electric current passes through the hollow portion of the core(7), the magnitude of the electric current is detected by the Hallelement (41).

Typically, the electric current detector in which the outer case ispreviously resin molded is adopted. After the core is accommodated in acore accommodating chamber formed in the outer case, a synthetic resin(e.g., an epoxy resin) is filled into the core accommodating chamber tofix the core into the outer case (see Patent Document 1).

In the assembling process of the electric current detector in which thesynthetic resin is filled into the outer case, first, the core isaccommodated in the core accommodating chamber in the outer case totemporarily fix the core into the outer case, and the synthetic resin isfilled into the outer case to fix the core into the outer case, therebyperforming electric insulation with respect to the core.

In this connection, in the electric current detector, the Hall elementis required to be precisely positioned in the magnetic gap of the core.

However, in the electric current detector in which the synthetic resinis filled into the outer case, a large space (clearance) is necessaryfor filling the synthetic resin into the outer case, resulting inincrease in size of the outer case. In addition, to ensure positioningaccuracy for temporarily fixing the core into the outer case, acomplicate configuration for forming a positioning projection on theinner surface of the case, or the like is necessary. The positioningoperation of the core is troublesome.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: Japanese Patent Laid-open Publication No. 2006-78255

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Accordingly, the applicant has developed the electric current detectorin which, as shown in FIG. 9, the core (7) is covered with mold resins(61), (62) to form the outer case (6) with the mold resins (61),(62).

In such an electric current detector, the complicate configuration andthe troublesome operation for temporarily fixing the core into the outercase are not necessary, thereby improving assembling accuracy.

However, in the electric current detector in which, as shown in FIG. 9,the core (7) is covered with the mold resins (61), (62), and the core(7) receives an external force from the surrounding resins at the timeof resin molding, thereby causing large hysteresis in a relation (BHcurve) between a coercive force (Hc) and a residual magnetic fluxdensity (Br).

In addition, fine dust can enter into the resins at the time of resinmolding, with the result that the dust is exposed on the surface of theouter case (6) to lower the yield due to poor appearance.

Accordingly, an object of the present invention intend to provide anelectric current detector which can reduce hysteresis without beingincreased in size, can precisely and easily position a core into anouter case, and can prevent the yield from being lowered, and a corecomponent used therefor.

Means for Solving the Problems

In an electric current detector according to the present invention, anannular core (2) having a magnetic gap G and an electromagneticconversion element which is located in the magnetic gap of the core (2)and detects a magnitude of an electric current passing through the core(2) are arranged in an outer case (1).

Here, in the core (2), a mold resin portion (3) which covers a surfaceof the core (2) over part of an overall length along a magnetic paththereof is molded at one or a plurality of portions along the magneticpath to configure an integral core component (20), the core component(20) being fixed into the outer case (1) in a state where a surface ofthe mold resin portion (3) makes contact with an inner surface of theouter case (1).

In the electric current detector of the present invention, after theouter case (1) and the core component (20) are previously manufacturedin individual processes, the core component (20) is fixed into the outercase (1).

In the core component (20), part of the overall length along themagnetic path of the core (2) is only covered with the mold resinportion (3). Therefore, a force that the core (2) receives from thesurroundings thereof at the time of molding the mold resin portion (3)is relatively small, thereby preventing hysteresis in the core (2) frombeing increased.

The outer case (1) and the core component (20) can obtain high accuracyin outer shape dimensions thereof by quality control in individual resinmolding processes. Therefore, in the process for fixing the corecomponent (20) into the outer case (1), the surface of the mold resinportion (3) is made in contact with the inner surface of the outer case(1), so that the core (2) can be precisely positioned into the outercase (1). In this state, the mold resin portion (3) is engaged into theouter case (1), so that the core component (20) is fixed into the outercase (1).

In addition, the outer case (1) is manufactured in the resin moldingprocess different from that of the core component (20), so that anyforeign particles such as dust can be prevented from entering into theresin which is the material of the outer case (1), thereby improving themanufacturing yield.

In a specific form, the core (2) has a polygonal shape having aplurality of corners, and the mold resin portion (3) is formed to coverat least one of the corners.

According to the specific form, the mold resin portion (3) is formed ata corner of the core (2), and the mold resin portion (3) makes contactwith the inner surface of the outer case (1) to position the corecomponent (20). Two surfaces of the mold resin portion (3) make closecontact with the inner surface of the outer case (1), thereby improvingpositioning accuracy.

A core component for an electric current detector according to thepresent invention includes an annular core (2) having a magnetic gap Gand a mold resin portion (3) which covers a surface of the core (2) overpart of an overall length along a magnetic path of the core (2), and amanufacturing method of the core component includes:

manufacturing an annular core member (21);

molding a mold resin portion (32) which covers a surface of the coremember (21) over part of an overall length along a magnetic path of themanufactured annular core member (21); and cutting the core member (21)and the mold resin portion (32) in a region in which the mold resinportion (32) is formed and forming the magnetic gap G and two mold resinportions (3 a), (3 b).

In the manufacturing method of the core component according to thepresent invention, after the mold resin portion (32) is molded on thecore member (21), the core member (21) and the mold resin portion (32)are cut to form the magnetic gap G. Therefore, when the core member (21)is a stacked type core member in which a plurality of electromagneticsteel plates are stacked, in the cutting process, the plurality ofelectromagnetic steel plates are constrained by the surroundings thereofby the mold resin portion (32), and are cut. This can avoid theseparation of some electromagnetic steel plates and the entering of anycutting pieces and metal burrs, which are caused by the cutting, intothe mold resin portion (32).

Effects of the Invention

The electric current detector according to the present invention and thecore component used therefor can reduce hysteresis without beingincreased in size, can precisely and easily position the core into theouter case, and can prevent the yield from being lowered.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an electric current detector accordingto the present invention.

FIG. 2 is a perspective view, partially broken away, of the electriccurrent detector.

FIG. 3 is a cross-sectional view taken along line A-A of FIG. 1.

FIG. 4 is a cross-sectional view taken along line B-B of FIG. 1.

FIG. 5 is a cross-sectional view taken along line C-C of FIG. 1.

FIG. 6 is an exploded perspective view of the electric current detectoraccording to the present invention.

FIG. 7 is a process diagram showing a manufacturing method of a corecomponent according to the present invention.

FIG. 8 is a diagram showing a plurality of arrangement forms of one or aplurality of mold resin portions with respect to a core member.

FIG. 9 is a cross-sectional view of a conventional electric currentdetector.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of the present invention will be specificallydescribed with reference to the drawings.

As shown in FIGS. 1 and 2, in an electric current detector according tothe present invention, the electric current detector accommodate a corecomponent (20) having a magnetic gap G, and a printed circuit board (4)having a Hall element (41) in an outer case (1) made of a syntheticresin.

As shown in FIG. 6, in the outer case (1), an inner peripheral wall (12)in a square tubular shape and a planar partitioning wall (13) areintegrally molded in an inner space surrounded by an outer peripheralwall 11 in a square tubular shape, the inner space being partitionedinto a core accommodating chamber (16) and a board accommodating chamber(17) by the partitioning wall (13). The partitioning wall (13) can beomitted.

A cutaway (14) is formed in the partitioning wall (13). In addition, oneor more slits (15), (15) (two slits in the embodiment) are formed ineach of the right and left wall surfaces of the outer peripheral wall(11).

The core component (20) has a core (2) having a substantially squareannular shape and the magnetic gap G, and four mold resin portions (3a), (3 b), (3 c), (3 d), which cover four corners of the core (2). Aprojection (31) is integrally formed on the side surface of a mold resinportion (3) so as to be engageable into the corresponding slit (15) inthe outer case (1).

The Hall element (41) is formed to be planar, and is erected verticallyon the surface of the printed circuit board (4). In addition, two screwholes (42), (42) are formed in both ends of the printed circuit board(4). The Hall element (41) can also be surface mounted on the printedcircuit board (4).

The core component (20) is accommodated in the core accommodatingchamber (16) in the outer case (1), and the printed circuit board (4) isaccommodated in the board accommodating chamber (17) in the outer case(1). In this state, the Hall element (41) passes through the cutaway(14) in the outer case (1), and is interposed in the magnetic gap G ofthe core component (20) (see FIGS. 3 to 5).

In the state where the core component (20) is accommodated in the coreaccommodating chamber (16) in the outer case (1), as shown in FIG. 3,four mold resin portions (3 a), (3 b), (3 c), (3 d) of the corecomponent (20) are provided at four corners of the core accommodatingchamber (16) in the outer case (1), respectively, and two surfaces ofthe mold resin portion (3) orthogonal to each other make contact withthe inner surface of the outer case (1). Thereby, the core component(20) is precisely positioned into the outer case (1).

As shown in FIG. 5, the projection (31) of the mold resin portion (3) isengaged into the slit (15) in the outer case (1), thereby fixing thecore component (20) into the outer case (1).

As shown in FIG. 2, the printed circuit board (4) is fixed into theouter case (1) by screwing two screws (5), (5) from the screw holes(42), (42) shown in FIG. 6 into the partitioning wall (13) in the outercase (1). Other fixing methods different from the fastening method usingthe screw (5) can also be adopted.

Thereby, the Hall element (41) is held in the precise position in themagnetic gap G of the core component (20).

FIG. 7 shows the manufacturing process of the core component (20)according to the present invention.

First, as shown in FIG. 7 (a), a core member (21) which has asubstantially square annular shape and four corners (21 a), (21 b), (21c), (21 d) is manufactured. The core member (21) is manufactured, forexample, by helically winding a belt-shaped electromagnetic plate.

Next, as shown in FIG. 7(b), a first mold resin portion (32) which has along rectangular parallelepiped shape and covers two corners (21 a), (21b) on the upper side of the core member (21), a second mold resinportion (33) which has a short rectangular parallelepiped shape andcovers one corner (21 c) on the lower side thereof, and a third moldresin portion (34) which has a short rectangular parallelepiped shapeand covers the other corner (21 d) on the lower side thereof are molded.Here, the projection (31) is integrally molded on the side surface ofeach of the mold resin portions.

Finally, the core member (21) and the first mold resin portion (32) arecut by a cutter (not shown) in the range of the first mold resin portion(32). Therefore, as shown in FIG. 7(c), the core component (20) whichhas the magnetic gap G and four mold resin portions (3 a), (3 b), (3 c),(3 d) is obtained.

The core component (20) and the printed circuit board (4), which havebeen obtained in such a manner are fixed into the separatelymanufactured outer case (1). Therefore, the electric current detector ofthe present invention shown in FIGS. 1 to 5 is completed.

Here, the resin for fixing the core component (20) is not filled intothe outer case (1).

FIG. 8 shows a plurality of arrangement forms of one or a plurality ofmold resin portions to be formed on the core member (21) before themagnetic gap is formed in the manufacturing process of the corecomponent according to the present invention. In these forms, a moldresin portion (35) which has a long rectangular parallelepiped shape iscut for forming the gap.

In the form of FIG. 8(a), three mold resin portions (35), (36), (37) areformed on the core member (21), and the two mold resin portions (36),(37) on the lower side each cover the corners of the core member (21).In addition, in the form of FIG. 8(b), the three mold resin portions(35), (36), (37) are formed on the core member (21), and each of themold resin portions (35), (36), (37) cover the corners of the coremember (21).

In the form of FIG. 8(c), three mold resin portions (35), (36), (37) areformed on the core member (21), and any mold resin portions (35), (36),(37) do not cover the corners of the core member (21). In addition, inthe form of FIG. 8(d), the three mold resin portions (35), (36), (37)are formed on the core member (21), and the mold resin portion (35) onthe upper side covers two corners of the core member (21).

In the form of FIG. 8(e), one mold resin portion (35) is formed on thecore member (21), and the mold resin portion (35) does not cover thecorners of the core member (21). In addition, in the form of FIG. 8(f),one mold resin portion (35) is formed on the core member (21), and themold resin portion (35) covers two corners of the core member (21).

Even when any of the forms is adopted, in the electric current detectoraccording to the present invention, the surface of the mold resinportion (3) makes close contact with the inner surface of the outer case(1). Thereby, the core component (20) is precisely positioned into theouter case (1).

Table 1 below shows the results obtained by measuring the coerciveforces (Hc) and the residual magnetic flux densities (Br) in theunmolded electric current detector in which after the core isaccommodated in the previously manufactured outer case, the resin isfilled into the outer case, the currently-used electric current detectorin which the core is covered with the mold resin to form the outer case,and the partially-molded electric current detector according to thepresent invention.

TABLE 1 Coercive force (Hc) Residual magnetic flux density (Br)Currently- Partially- Currently- Partially- Unmolded used moldedUnmolded used molded electric electric electric electric electricelectric current current current current current current detectordetector detector detector detector detector 237.1 310.1 224 41.8 62.242.0 226.9 282.1 231 41.5 61.9 41.8 246.3 311.3 237 43.0 60.9 44.9 225.0291.7 226 40.5 62.3 42.0 225.8 277.4 225 40.3 58.2 41.8 228.0 293.4 22639.7 63.2 42.3 227.6 304.8 238 40.8 59.8 43.6 222.2 296.2 211 39.2 63.739.4 (Average values) 229.9 295.9 227.1 40.8 61.5 42.2 (Comparison) 100%128.7% 98.8% 100% 150.6% 103.4%

As is apparent from Table 1, in the partially-molded electric currentdetector according to the present invention, the same magneticcharacteristic as the conventional unmolded electric current detector ismaintained, and hysteresis caused by the action of an external force atthe time of resin molding is not increased.

On the contrary, the coercive force (Hc) and the residual magnetic fluxdensity (Br) in the currently-used electric current detector are about30% to 50% higher than those in the unmolded electric current detector,resulting in increasing hysteresis.

In this way, in the partially-molded electric current detector accordingto the present invention, part of the overall length along the magneticpath of the core (2) is only covered with the mold resin portion (3).Therefore, a force that the core (2) receives from the surroundingsthereof at the time of molding the mold resin portion (3) is relativelysmaller than that in the currently-used electric current detector,thereby preventing hysteresis from being increased.

In addition, in the electric current detector according to the presentinvention, the outer case (1) and the core component (20) can obtain ahigh accuracy in the outer shape dimensions thereof by the qualitycontrol in individual resin molding processes. Therefore, in the processfor fixing the core component (20) into the outer case (1), the surfaceof the mold resin portion (3) is made in contact with the inner surfaceof the outer case (1), so that the core (2) can be precisely positionedinto the outer case (1).

In addition, the outer case (1) is manufactured in the resin moldingprocess different from that of the core component (20), so that anyforeign particles such as dust can be prevented from entering into theresin which is the material of the outer case (1), thereby improving themanufacturing yield.

Further, in the manufacturing method of the core component according tothe present invention, after the mold resin portion (32) is molded onthe core member (21), the core member (21) and the mold resin portion(32) are cut to form the magnetic gap G. Therefore, when the core member(21) is a stacked type core member in which a plurality ofelectromagnetic steel plates are stacked, in the cutting process, theplurality of electromagnetic steel plates are constrained by thesurroundings thereof by the mold resin portion (32), and are cut. Thiscan avoid the separation of some electromagnetic steel plates and theentering of any magnetic particles, which are caused by the cutting,into the mold resin portion (32).

The configurations of the respective portions of the present inventionare not limited to the above embodiment, and various modifications canbe made within the technical range of the claims. For example, variousconfigurations in which the core component (20) is fixed into the outercase (1), other than the configuration manufactured by adhesion withresin filling can be adopted without being limited to the engagingconfiguration of the slit (15) in the outer case (1) and the projection(31) on the core component (20).

DESCRIPTION OF REFERENCE CHARACTERS

-   (1) Outer case-   (16) Core accommodating chamber-   (17) Board accommodating chamber-   (20) Core component-   (G) Magnetic gap-   (2) Core-   (3) Mold resin portion-   (4) Printed circuit board-   (41) Hall element

The invention claimed is:
 1. A core component for an electric currentdetector, the core component comprising a polygonal-shaped core having acentral opening, the core being in part covered with mold resin: whereinsaid core comprises a plurality of corners and a plurality of linearportions extending between said corners to define said polygonal shapedcore, wherein one of the linear portions is a first linear portionhaving a magnetic gap, said first linear portion being covered on anouter peripheral surface thereof with mold resin with the exception ofthe magnetic gap, which is not covered with mold resin, and the cornersnot directly adjacent to said first linear portion are not covered withmold resin.
 2. The core component according to claim 1, wherein at leastone of said plurality of linear portions, except for said first linearportion, is in part covered on an outer peripheral surface thereof withmold resin.